Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Patent
1984-11-19
1987-06-30
Willis, Davis L.
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
156626, 356357, G01B 402
Patent
active
046766448
ABSTRACT:
A device for monitoring the thickness of a low absorption thin film or layer (53B) on an at least partially reflecting substrate (31) placed inside a vacuum chamber (1) closed by a window (7), includes a polarized laser source (8), a polarizing cube (13), placed in the path of the laser beam, consisting of two right-angle prisms (13A, 13B) assembled by their hypotenuse faces by means of a dielectric film (13C), the cube being oriented so that the incident laser beam has a 45 degree angle of incidence with the film, the cube allowing a first part of the incident beam to pass into a first, linear optoelectronic converter (15A) supplying a first electrical signal (I.sub.oe), the cube reflecting a second part of the incident beam to pass through a quarter-wave plate (7, 7A) and reflect off the layer before returning through the cube, without being deflected, and thereafter striking a second converter (15B) supplying a second electrical signal (I.sub.e). The device further includes apparatus for finding the ratio of the second electrical signal to the second electrical signal, for correcting spurious light, or obtaining the derivative of the ratio, for calibrating the measuring head, and for supplying a signal when the derivative has remained, for a given amount of time, between two given values limiting a set point value for the desired thickness of the layer.
REFERENCES:
patent: 4367044 (1983-01-01), Booth, Jr. et al.
Bennett et al., "SElective and Directional Etching of Polysilicon and WSi.sub.2 ", IBM Tech. Disclos. Bull., vol. 25, No. 1, pp. 33-34, 6/82.
Compagnie Industrielle Des Telecommunications
Koren Matthew W.
Willis Davis L.
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